A motherboard of a notebook computer is generally provided with a central processing unit (CPU) platform, a chipset and some peripheral circuits. As known, Intel and AMD are two of the most important manufacturers of CPU platforms. Currently, the motherboards and the chipsets of the systematic companies are designed according to the specifications provided by the CPU manufacturers. In other words, the systematic companies have no choice but to comply with these stringent specifications, including the voltage specifications.
Conventionally, a CPU core voltage switching circuit is provided by the CPU manufacturer to produce various voltages. After the chipset is communicated with a specified CPU platform, the chipset will realize the working voltage required for the operating CPU platform according to the information registered on the CPU platform by the CPU manufacturer. Consequently, the CPU core voltage switching circuit offers the desired working voltage to the CPU platform.
The CPU core voltage switching circuit, however, has some drawbacks. For example, after the desired working voltage is selected from the various voltages, the rejected voltages are not used. Since only one working voltage is desired, the function of producing various voltages cause extra cost. Recently, a project of producing hundred-dollar laptop computers has been proposed by Massachusetts Institute of Technology and a low-cost netbook computer Eee PC has been designed by ASUSTeK Computer Inc. For producing these cheap educational devices, any measure to cost down will be well received.
Therefore, there is a need of providing a CPU core voltage supply circuit to obviate the drawbacks encountered from the prior art.